.beta. type titanium alloys such as Ti-15%V-3%Cr-3%Sn-3%Al, or Ti-3%Al-8%V-6%CR-4%Mo-4%Zr are excellent in cold workability, and are sometimes used for cold rolled thin plates, cold drawn bars or wire materials. The strength of these .beta. type titanium alloy materials is increased as the degree of cold working is increased. As a result, for example, in Ti-15%V-3%Cr-3%Sn-3%Al alloy, the maximum strength may exceed 165 kgf/mm.sup.2. However, elongation in this case is at most about 1%. Since the ductility is decreased as the strength is increased, heat treating conditions are selected which may maintain the elongation value while controlling the strength in practice.
The cold worked material of .beta. type titanium alloy is subjected to the solution treatment--aging treatment after the cold working, or the cold working--aging treatment. If the cold worked strain is kept as cold worked or the solution temperature is low enough to retain most of the cold worked strain, precipitation of crystal is accelerated and refined in the aging, so that it is possible to increase the strength while increasing the cold reduction. On the other hand, since the precipitation of .alpha. phase particle in the grain boundary is remarkably expedited in comparison with interiors of the crystal grain together with increasing the degree of cold working, the grain boundary is easily destroyed as the degree of cold working is decreased. Therefore, in the cold worked material by the prior art, the strengh is limited to the 165 Kgf/mm.sup.2, and the high strength material has low elongation value.
The present invention is to provide a method for producing titanium alloy materials without conventional defects.
It is an object of the invention to provide a method for producing .beta. type titanium alloy materials enriched with high strength and ductility.
It is another object of the invention to provide a method for producing .beta. type titanium alloy materials having high strength and ductility, irrespectively of plate thickness.